I have noticed it's more generally the norm these days, although it still varies person to person. I'm only three years older than Letby and insisted on my independence! I'm the third of four children, the other three being boys. My two older brothers were born a year apart, then there was a five year age gap before me, and my younger brother arrived two and a half years after me. So me and brother number 3 were "the babies", and had one or two teachers sneer at us for being spoilt and mollycoddled - not based on anything we'd done, but just stereotyping, and automatically treated us like we'd be naughtier than the other kids. Well, I wasn't perfect and could be as naughty as any kid, but "mollycoddled" was an insult and a stereotype I rebelled against! Once I was 16, I would never let my mum get involved in anything, even if she offered; and I left Birmingham to live in London as soon as I'd done my GCSEs. I think that stereotyping what fuelled my drive for independence, and my brother is similar although he left home relatively later at 23, because he was the last one to fly the nest and he thought it would break Mum's heart. It didn't, though! She'd remarried by then and she was practically nagging him to make a life for himself with his girlfriend, as she knew that's what he wanted. They now live in Wales and only regret not doing it sooner.
However, I think we're probably anamolies among our age group. I agree there's a lot more parental involvement for a lot longer now, in general. When I was temping during the 2009 recession, one of the offices I went to work at was full of people my age but from much more privileged backgrounds. They were friendly enough, in a nosy way, and asked a lot of questions! When discussing what we'd done after one weekend, I mentioned I'd gone to my mum's in Birmingham. My colleagues were horrified that a) I didn't have a car to drive there and "had to" get the train instead, and that b) I'd paid for my own ticket instead of Mum buying it for me! I was 22, well into adulthood. To me, once you were of working age, you'd grab your chance to earn your own money and pay for your own stuff because then you didn't have to owe anything. I couldn't understand why a healthy adult would choose to rely on their parents at that age. I'd never really come across that attitude before and it struck me that might have been their first time meeting a working-class person. So it could be partly a class thing with Letby, I guess. Her dad was a boss in his company and might have been used to getting his own way? Who knows. Maybe that, combined with how good she felt getting away with murder - literally.